Recently, with increasing development of information industries, portable information devices such as notebook computers, mobile phones or personal digital assistants are widely used in many instances. In a case that a portable information device is used in a dim environment, the numbers and the characters marked on the keys of the keyboard of the portable information device are not clearly visible. In other words, the dim environment becomes hindrance from operating the keyboard. In addition, if the numbers and the characters marked on the keys of the keyboard are reluctantly viewed in the dim environment, the user is readily suffered from vision impairment. For solving these drawbacks, a luminous keyboard has been disclosed. The luminous keyboard can be used in the dim environment in order to enhance the applications thereof. Moreover, by changing the layout of the luminous regions of the luminous keyboard, the information device having the luminous keyboard is more aesthetically-pleasing and thus the competitiveness thereof is enhanced.
FIG. 1 is a schematic cross-sectional view illustrating a conventional luminous keyboard. As shown in FIG. 1, the luminous keyboard 1 comprises a reflector 11, a light guide plate 12, a supporting plate 13, a membrane wiring board 14, plural keys 15, and plural lateral-emitting type illumination elements 16. The membrane wiring board 14 comprises a lower wiring plate 141, an upper wiring plate 142, and an intermediate plate 143. The intermediate plate 143 is arranged between the lower wiring plate 141 and the upper wiring plate 142. The lower wiring plate 141, the intermediate plate 143 and the upper wiring plate 142 are all made of transparent light-guiding material. The transparent light-guiding material includes for example polycarbonate (PC) or polyethylene terephthalate (PET).
Please refer to FIG. 2, which is a schematic exploded view illustrating a membrane wiring board of the conventional luminous keyboard of FIG. 1. The lower wiring plate 141 comprises a first circuit pattern 1411. The first circuit pattern 1411 comprises plural silver paste conductive element lines 14111 and plural lower contacts 14112. The upper wiring plate 142 comprises a second circuit pattern 1421. The second circuit pattern 1421 comprises plural silver paste conductive element lines 14211 and plural upper contacts 14212. The intermediate plate 143 comprises plural perforations 1431 corresponding to the plural lower contacts 14112 and the plural upper contacts 14212, respectively. Each of the upper contacts 14212 and the corresponding lower contacts 14112 are collectively defined as a membrane switch 144.
The supporting plate 13 is disposed under the membrane wiring board 14. In addition, the supporting plate 13 comprises plural openings 131, a first fixing structure 132, and a second fixing structure 133. Each of the keys 15 comprises a keycap 151, an elastic element 152, and a scissors-type connecting element 153. The keycap 151 comprises a first keycap connecting structure 1511 and a second keycap connecting structure 1512. The scissors-type connecting element 153 comprises a first frame 1531 and a second frame 1532. In addition, the elastic element 152 is arranged between the keycap 151 and the membrane wiring board 14.
The membrane wiring board 14 further comprises apertures 145 and 146 (see FIG. 1). The first fixing structure 132 and the second fixing structure 133 are penetrated through the apertures 145 and 146, respectively. A first end 15311 of the first frame 1531 is connected to the second fixing structure 133, and a second end 15312 of the first frame 1531 is connected to the first keycap connecting structure 1511. In addition, a first end 15321 of the second frame 1532 is connected to the first fixing structure 132, and a second end 15322 of the second frame 1532 is connected to the second keycap connecting structure 1512.
As any key 15 is depressed and moved downwardly relative to the supporting plate 13, the first frame 1531 and the second frame 1532 of the scissors-type connecting element 153 are switched from an open-scissors state to a folded state. Moreover, as the keycap 151 is moved downwardly to compress the elastic element 152, the corresponding upper contact 14212 is pushed by the elastic element 152. Consequently, the upper contact 14212 is penetrated through the corresponding perforation 1431 to be contacted with the corresponding lower contact 14112. Consequently, the corresponding membrane switch 144 is electrically conducted, and the luminous keyboard 1 generates the corresponding key signal. When the depressing force exerted on the key 15 is eliminated, an elastic force provided by the elastic element 152 is acted on the keycap 151. In response to the elastic force, the keycap 151 is moved upwardly relative to the supporting plate 13. Meanwhile, the first frame 1531 and the second frame 1532 of the scissors-type connecting element 153 are switched from the folded state to the open-scissors state, and the keycap 151 is returned to its original position.
Moreover, the lateral-emitting type illumination elements 16 are located at bilateral sides of the light guide plate 12 for emitting light beams. The light beams are incident into the light guide plate 12. The light guide plate 12 is disposed on the reflector 11. Plural light-guiding dots 121 are formed on a bottom surface of the light guide plate 12 for collecting and scattering the light beams. The light-guiding dots 121 are aligned with corresponding keys 15. After the light beams are incident into the light guide plate 12, the light beams are diffused into the whole light guide plate 12. Due to the ink properties of the light-guiding dots 121, the light beams will be scattered upwardly and downwardly. The portions of the light beams that are scattered upwardly will be sequentially transmitted through the openings 131 of the supporting plate 13 and the membrane wiring board 14 and then projected to the plural keys 15. The portions of the light beams that are scattered downwardly will be reflected by the reflector 11, and the reflected light beams are directed upwardly. Consequently, the light beams provided by the illumination elements 16 can be well utilized to illuminate the plural keys 15. However, the conventional luminous keyboard 1 still has the following drawbacks.
Firstly, although the reflector 11 can facilitate the light beams which are scattered downwardly from the light-guiding dots 121 to be reflected upwardly, a small amount of the light beams which are scattered downwardly from the light-guiding dots 121 may be transmitted through the reflector 11 because of the material of the reflector 11 of the conventional luminous keyboard 1. Under this circumstance, a portion of the light amount is lost.
Secondly, although the light beams can be diffused into the whole light guide plate 12 after the light beams are incident into the light guide plate 12, the light amount of the region farther from the lateral-emitting type illumination element 16 is less than the light amount of the region closer to the lateral-emitting type illumination element 16 because portions of the light beams have been reflected out of the light guide plate 12 by the light-guiding dot 121 closer to the lateral-emitting type illumination element 16.
Thirdly, since the travelling distance of the scissors-type connecting element 153 is long, the luminous keyboard 1 should have sufficient space to allow normal operations of the scissors-type connecting element 153. The necessary space is detrimental to the reduction of the thickness of the luminous keyboard 1. In other words, the conventional luminous keyboard 1 fails to meet the requirements of light weightiness, slimness and miniaturization.
In views of the first drawback and the second drawback, the uses of the lateral-emitting type illumination elements 16 and the light guide plate 12 of the conventional luminous keyboard 1 can illuminate the plural keys 15, but the light utilization efficiency is insufficient. For improving the light utilization efficiency, the lateral-emitting type illumination elements 16 may be replaced by bottom-emitting type illumination elements. The bottom-emitting type illumination elements are disposed under the keys 15 for providing light beams to the keys directly, so that the light utilization efficiency is enhanced. However, since the bottom-emitting type illumination element is disposed under the elastic element 152, the compressible extent of the elastic element 152 is restricted by the bottom-emitting type illumination element. If the compressible extent of the elastic element 152 is insufficient, the action of depressing the keycap 151 fails to result in the electrical conduction of the corresponding membrane switch 144. In other words, the uses of the bottom-emitting type illumination elements to replace the lateral-emitting type illumination elements 16 and to provide the light beams to the keys 15 directly can not be effectively applied to the improvement of the conventional luminous keyboard 1.
Recently, a capacitive sensing keyboard is disclosed. The capacitive sensing keyboard can solve the third drawback of the conventional luminous keyboard 1. As the keycap is depressed, the electric field of a circuit board of the capacitive sensing keyboard is changed. In response to the change of the electric field, the circuit board generates a corresponding key signal. Since the scissors-type connecting element is not an essential component of the capacitive sensing keyboard, if the scissors-type connecting element is not used, the overall thickness of the capacitive sensing keyboard is effectively reduced. However, since the current capacitive sensing keyboard has no illuminating function, if the capacitive sensing keyboard is used in the dim environment, some problems occur. For example, since the numbers and the characters marked on the keys of the capacitive sensing keyboard are not clearly visible, the dim environment becomes hindrance from operating the capacitive sensing keyboard or the user is readily suffered from vision impairment.